1. Field of the Invention
The present invention pertains to a hydraulic bidirectional drilling jar insertable in a drill stem for delivering impact blows in an upward or downward direction to the drill stem.
2. Background Art
In the art of drilling jars for delivering blows to a drill stem or to components lodged in a well bore, there have been several inventions directed to providing a tool which utilizes a hydraulic dashpot arrangement wherein, when the tool is interposed in the drill stem, a predetermined force may be imposed on the tool and, upon sudden release of a trapped quantity of hydraulic fluid within the tool mechanism, an impact blow is delivered to the drill stem.
One of the problems with prior art hydraulic type drilling jars pertains to the arrangement of relatively moving parts which provide, in effect, an orifice to restrict the flow of hydraulic fluid during the cocking action of the jar. Known types of hydraulically actuated drilling jars such as that disclosed in U.S. Pat. No. 2,802,703 rely on predetermined clearances between the relatively moving parts to control the flow of hydraulic fluid and the "dashpot" action. Unfortunately, the cooperating parts which provide the control orifices for the hydraulic dashpot are also working parts which are subject to manufacturing tolerances on the part dimensions and to wear in use whereupon the clearance between the parts varies so that the operating characteristics of the hydraulic dashpot are also subject to variation. A tool such as the type disclosed in the aforementioned patent is also subject to malfunction due to the reliance on movement of tool components under forces which cannot be easily controlled to enable resetting of the tool. The problems associated with prior art drilling jars cannot be tolerated particularly in jars that are employed in a working drill stem in deep hole drilling, for example, where the reliability and operating characteristics of a downhole tool must be given special consideration.
Another disadvantage with certain types of prior art hydraulic drilling jars pertains to the unidirectional characteristics of these jars, that is, they are capable of delivering an impact blow in only one direction and must be coupled with a second jar of either the mechanical or hydraulic type to provide bidirectional jarring capability. Such arrangements are expensive and suffer from the inherent disadvantage of adding still further complicated mechanism to the drill stem downhole. Yet another problem with prior art drilling jars pertains to: (1) the uncertainty of the relative positions of the parts of the jar during the resetting or recocking operation, (2) the distance over which the mechanism must be moved to reset the jar, and (3) the length of time required to reset the jar for another blow.
In order to overcome one of the problems inherent with prior art drilling jars which rely on orifices or restrictions provided by relatively moving parts, it was determined in pursuing the present invention, that it would be desirable to develop a substantially positive mechanical seal capable of withstanding the pressure and temperature conditions of a typical operating environment of drilling jars. Until the development of the present invention, satisfactory seal arrangements and hydraulic dashpot arrangements for downhole drilling jars have gone unfulfilled. The development of a tool which is adapted for either intermittent or continuous use in a drill stem, which is easily serviced and repaired, is adapted for rapid cocking and tripping, and is economical to manufacture has heretofore eluded workers in the drilling jar art. Moreover, those familiar with the art of downhole tools in the well drilling industry readily appreciate the desire and need for a drilling jar which is mechanically uncomplicated, is relatively compact, has bidirectonal capability and is capable of repeated use without malfunction or without uncontrolled variation in the blow intensity.